From a perspective of a weight reduction of a petrol engine for a vehicle and from a perspective of increases of thermal insulating properties and design flexibility of the petrol engine, an intake manifold distributing air sucked by the engine into cylinders has been mainly made of resin instead of metal such as aluminum alloy in recent years. However, when a resin is applied as a material of the intake manifold, the form accuracy tends to deteriorate because warpage or shrinkage of the resin is unavoidable, compared to an intake manifold made of metal.
For example, a four-cylinder engine includes an intake manifold having four air intake passages. Further, the air intake manifold includes an air intake apparatus controlling an air intake volume and a flow rate or direction of air sucked into the air intake passages when needed. The air intake apparatus includes open/close valves opened and closed by a shaft in the respective air intake passages in accordance with rotation of the shaft. Opening of the open/close valve is controlled by an actuator so that an appropriate combustion condition is obtained depending on driving states of a vehicle.
For example, an air intake apparatus for an internal combustion engine described in JP2006-233907A (hereinafter referred to as Patent document 1) includes a plurality of resin control units serving as a valve opening/closing mechanism. Each of the control units is arranged in a receiving portion of an intake manifold attached to a cylinder head, thereby opening and closing each air intake passage of the intake manifold. The control unit includes a housing (cartridge) and an open/close valve rotatably supported in the housing. The housing of the control unit is inserted in the receiving portion of the intake manifold while having a predetermined clearance defined between an outer surface of the housing and the receiving portion. Accordingly, the housing is retained to the intake manifold via elastic members.
However, according to the Patent document 1, when the intake manifold is expanded due to heat or deformed due to a dimensional change caused by water absorption, the housing of the control unit is deformed via the elastic members. Accordingly, the housing may be cracked and damaged due to stress generated by the deformation of the control unit. When the housing is deformed, scoring or scratches of the open/close valve arranged in the housing occurs, so hat a bearing of the shaft is not precisely aligned to a desired position. Consequently, when the open/close valve is opened and closed by the shaft in accordance with the rotation of the shaft, a slide resistance of the open/close valve and abrasions of the bearing may incase. Moreover, when a clearance between the housing and the open/close valve is increased, a seal performance of the open/close valve may deteriorate when the open/close valve is in a fully closed state.
In addition, when the cylinder head and the housing make contact with each other, stress is generated in the housing. Accordingly, the housing may be cracked and damaged. Additionally, when a clearance for preventing the stress is established between the cylinder head and the housing, the housing is moved in the clearance during an activation of the engine. As a result, an abnormal noise may occur and durability of the control unit may deteriorate.
A need thus exists for an air intake apparatus for an internal combustion engine, which is not susceptible to the drawback mentioned above.